The present invention relates generally to a cassette or cartridge for housing a printing film in the form of a tape or ribbon wound around bobbins or reels, and to a method of feeding the printing film. More particularly, the invention relates to a cassette for transfer printing film to be used by loading the same into a thermal transfer printer, and to a method of feeding the printing film.
Heretofore, in order to facilitate the loading of transfer printing film into a thermal transfer printer, cassettes for transfer printing film have been widely used. Each of these cassettes accommodates a reel on the film-feed side for holding a roll of transfer printing film and another reel on the film-takeup side for winding and taking up the transfer printing film fed from the feed reel. When the cassette holding the transfer printing film is loaded into a printer, the reel on the take-up side is coupled to a driving shaft or spindle of the printer.
The transfer printing film in the cassette thus loaded is used as it is paid out or unwound from the feed reel and taken up or wound by the take-up reel. As will be described more fully hereinafter with respect to an example and in conjunction with a drawing, the diameters of the film rolls on the feed and take-up reels respectively differ considerably between the start and end of use of the film. Because of this difference, torque balance of the driving shaft of the printer cannot be maintained, whereby fluctuations in the tension of the film become large. Consequently, printing trouble such as color shifting, creasing or wrinkling, ribbing, and scoring tends to occur.
It may appear that this problem can be overcome by adjusting the driving torque on the printer side. This measure, however, is undesirable because it would complicate the printer mechanism and increase the cost.
U.S. Pat. No. 4,978,240 to Hiroshi Katsuno et al discloses a cassette for ink ribbon, having a cassette case including resilient pressing tabs for braking the feed reel. The pressing tabs are constantly in sliding contact with the reel so that torque balance can not always be obtained.